Technology that three-dimensionally recognizes images photographed with a camera has been recently put into practical use. This technology is used to, for example, create a spherical image or another image that covers the entire periphery in a vehicle by using images photographed with an on-board camera mounted on the vehicle. The technology is also used to create an image that enables the position of the robot relative to a target to be determined by using images photographed with a camera mounted on a robot.
When a three-dimensionally image is created from images photographed with a camera by using the technology that three-dimensionally recognizes images photographed with a camera, information about the pose and position of the installed camera may need to have been correctly grasped. Known technology 1 and known technology 2 described below are used to estimate information about the pose and position of an installed camera.
Above-mentioned known technology 1 will be described with reference to FIG. 17. FIG. 17 is a drawing that illustrates known technology 1. In known technology 1, objects such as markers are first placed in prescribed positions in the real space, in other words, prescribed positions in the world coordinate system, and photographed with a camera. Then, known technology 1 extracts three points (Po, P1, P2) corresponding to three points (xo, x1, x2) on an image plane H obtained by photographing the markers, as depicted in FIG. 17. These three points (Po, P1, P2) are three-dimensional positions, corresponding to three points (xo, x1, x2) on the image plane H, in a camera coordinate system. Known technology 1 creates simultaneous equations to formulate the surfaces of a triangular pyramid, which is formed by interconnecting three points (Po, P1, P2) and the origin C of the camera coordinate system, as depicted in FIG. 17. For example, the surfaces of the triangular pyramid formed by interconnecting three points (Po, P1, P2) and the origin C can be represented by formulated equations according to the cosine formula. Simultaneous equations (1) indicated below are created from these formulated equations. The distance between the origin C and point Po will be denoted Lo, the distance between the origin C and point P1 will be denoted L1, the distance between the origin C and point P2 will be denoted L2, the eye line vector from origin C to point Po will be denoted Vo, the eye line vector from origin C to point P1 will be denoted V1, and the eye line vector from origin C to point P2 will be denoted V2. The eye line vectors (Vo, V1, V2) are obtained from the optical axis position and focal length of the camera and other internal parameters. <(Vi, Vj) (i, j=0, 1, 2, i≠j) in equation (1) below represents the inner product of vector Vi and vector Vj. D0,1, D0,2, and D1,2 in equation (1) each represent an actual distance between two points among points Po to P2.[Equation 1]L02+L12+2L0L1v0,v1=D0,12 L02+L22+2L0L2v0,v2=D0,22 L12+L22+2L1L2v1,v2=D1,22  (1)
Next, know technology 1 obtains the solution of the quartic equation derived from the above simultaneous equations (1) to obtain distances Lo, L1, and L2 from the origin C in the camera coordinate system in FIG. 17 to three points (Po, P1, P2). Know technology 1 then uses the distances from the origin C to three points (Po, P1, P2) and eye vectors (Vo, V1, V2) obtained from the internal parameters of the camera to derive the position and pose of the camera by an inverse operation.
Alternatively, known technology 2, for example, extracts feature points on an image on which objects such as markers are photographed with a camera, and sets a search area corresponding to a substantially estimated position of the camera on the basis of the correspondence between the feature points on the image and the view patterns of the objects. Known technology 2 then searches the search area for an optimum solution that meets required error precision for a total six parameters related to the position and pose of the camera to detect the position and pose of the camera.    Japanese Laid-open Patent Publication No. 6-258028 is an example of related art.    Quan and Lan, “Linear N-Point Camera Pose Determination”, IEEE trans. on PAMI, 1999 is another example of related art.